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Liver phase 1 > Liver detoxification > Flashcards

Liver detoxification Flashcards

1
Q

What are xenobiotics?

A

Foreign chemical substances that are not normally found or produced in the body. They are detoxified to be made safer. Drugs are considered xenobiotics. They’re excreted in urine, bile, sweat and breath.

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2
Q

Where does detoxification occur?

A

Most of the metabolism of xenobiotics occurs in the liver but some take place in the lungs and small intestine before compounds are absorbed into the bloodstream.

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3
Q

Where does biotransformation occur in the liver?

A

The smooth endoplasmic reticulum

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4
Q

What are the common features of cytochrome p450 enzymes?

A
  • present in the smooth endoplasmic reticulum
  • oxidase the substrate and reduce oxygen to form water
  • Inducible
  • generate a reactive free radical compound
  • have a cytochrome reductase subunit which uses NAPDH.
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5
Q

What are cytochrome p450 enzymes?

A

Cellular proteins containing one or more heam groups involved in electron transfer.

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6
Q

What is the importance of pharmacologically active compounds being lipophilic?

A

It enables them to pass through plasma membranes to reach metabolising enzymes.

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7
Q

At what pH are pharmacologically active compounds non-ionised?

A

pH 7.4

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8
Q

How are pharmacologically active compounds transported in the blood?

A

Bound to plasma proteins.

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9
Q

Where are microsomal enzymes (cytochrome P450) located?

A

Smooth ER.

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10
Q

Which type of enzymes can have their activity induced or inhibited?

A

Microsomal enzymes

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11
Q

What can induce or inhibit microsomal enzymes?

A

Drugs, food, age, bacteria, alcohol.

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12
Q

Where are non-microsomal enzymes located?

A

Cytoplasm and mitochondria.

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13
Q

What reactions are non-microsomal enzymes involved in?

A

All conjugation reactions except glucuronidation!

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14
Q

What are the mechanisms for drug metabolism?

A

Phase 1 and phase 2 reactions. They usually occur sequentially. The aim is to make drugs more polar.

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15
Q

What is the aim of drug metabolism?

A

To make drugs more polar

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16
Q

Where does drug metabolism mostly occur?

A

In the liver where the enzymes are

17
Q

What is a phase 1 reaction?

A
  • Non-synthetic catabolic reaction: oxidation, reduction and hydrolysis.
  • Introduces a reactive group to the drug, this is the attack point for conjugation.
18
Q

Phase 1 reactions: what can happen in an oxidation reaction?

A
  • Hydroxylation (add OH group).
  • Dealkylation (remove CH side chains).
  • Deamination (remove NH).
  • Hydrogen removal.
19
Q

Phase 1 reactions: what can happen in a reduction reaction?

A

Add hydrogen, saturate unsaturated bonds.

20
Q

Phase 1 reactions: what can happen in a hydrolysis reaction?

A

Split peptide and ester bonds.

21
Q

What usually catalyses phase 1 reactions?

A

Cytochrome P450.

22
Q

What type of enzyme is cytochrome P450?

A

Microsomal

23
Q

Give examples of non-microsomal enzymes.

A

Oxidases, esterases, conjugases.

24
Q

What is a phase 2 reaction?

A
  • Synthetic anabolic reactions: conjugation, glucuronidation etc.
  • Usually inactivate products and increase hydrophilicity for renal excretion.
25
Q

What enzyme catalyses glucuronidation reactions?

A

Glucuronosyltransferase (UGT)

26
Q

What kind of enzyme is Glucuronosyltransferase?

A

Microsomal.

27
Q

Is Glucuronosyltransferase involved in phase 1 or phase 2 reactions?

A

Phase 2

28
Q

What other reaction is Glucuronosyltransferase involved in?

A

The conjugation of bilirubin.

29
Q

What is the effect on the efficacy of a drug if microsomal enzymes are induced?

A

The efficacy of the drug will reduce because the inducer will cause increased metabolism by microsomal enzymes.

30
Q

What is aspirin hydrolysed into?

A

Salcylic acid and ethanoic acid.

31
Q

What happens to aspirin in phase 2 metabolism?

A

It is conjugated with glycine or glucuronic acid and excreted in urine

32
Q

What happens in a glucuronidation reaction?

A

Glucuronic acid is added to conjugate a substrate. UDPGA is needed for this. Catalyst: glucuronyltransferase.

33
Q

What is the purpose of conjugating bilirubin?

A

It increases its water solubility for excretion.

34
Q

What type of bonds are broken in a phase 1 drug hydrolysis reaction?

A

Amide and ester bonds.

Liver phase 1 (10 decks)

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